(1) Field of the Invention
The present invention pertains to a motorized conveyor pulley of the type comprising a cylindrical pulley drum with axially opposite end plates enclosing an electric motor and drive transmission. The end plates of the pulley are mounted on a pair of shaft ends that pass through the end plates at the axially opposite ends of the pulley and support the motor and drive transmission in the pulley. In particular, the present invention pertains to the pair of end plates of the pulley that are constructed with an increased axial thickness compared to prior art end plates and are supported on the pair of shaft ends by pairs of bearings and are sealed by a pair of lubricant seals between each pair of bearings. The enlarged end plates and the pairs of bearings resist bending loads exerted on the conveyor pulley by the conveyor belt and thereby reduce loading stresses on the motor and drive transmission contained in the pulley permitting more economical manufacture of the motor and drive transmission.
(2) Description of the Related Art
A motorized conveyor pulley is employed at one end of a flat, continuous belt conveyor where the belt of the conveyor is looped or wrapped over the motorized conveyor pulley at one end of the conveyor and wrapped over an idler pulley at an opposite end of the conveyor. In order to provide sufficient friction engagement between the pair of pulleys and the belt to avoid slipping of the belt on the pulleys when the belt is conveying a substantial load, the belt is usually stretched very tight between the pair of pulleys resulting in a substantial load exerted on the pulleys by the belt.
The load exerted by the belt on the motorized conveyor pulley is transferred to the component parts contained inside the pulley. A typical motorized conveyor pulley includes a cylindrical pulley drum having a hollow interior. A pair of circular end plates close off the axially opposite ends of the drum. The end plates have coaxial center bores and stationary stub shafts extend through the center bores. Each stub shaft has a bearing mounted on its exterior that is received in the center bore of one of the end plates, thereby mounting the pulley drum for rotation on the stationary stub shafts.
Contained inside the pulley drum is an electric motor and a gear carrier that are mounted stationary to the ends of the two stub shafts projecting into the interior of the pulley drum. The electric motor drives a gear transmission mounted on the gear carrier that in turn drives a ring gear mounted on the interior of one of the pulley end plates imparting rotation to the pulley drum. The pulley drum contains a bath of lubricant, at times filling half the interior volume of the drum, that both cools and lubricates the motor and the transmission gearing.
The substantial load exerted on the motorized conveyor pulley by the conveyor belt causes the pulley to bend between the ends of the stub shafts projecting from the axially opposite ends of the pulley drum. The bending of the pulley drum is transferred through the end plates to the internal components of the motorized conveyor pulley. This at times would result in the bending of the gear carrier in the interior of the pulley drum which would result in gears of the transmission coming out of mesh, excessive gear chatter or gear noise and at times the breaking of gear teeth. The bending of the drum would also result in the leakage of lubricant past lip seals mounted on the stub shafts in the center bores of the pulley end plates.
The prior art solution to the bending transferred to the internal components of the pulley was to beef up the construction of the internal components. For example, the end shield of the motor to which the gear carrier of the transmission was attached would be constructed of cast iron or other cast metal with an increased thickness to resist the bending of the end shield. In addition, the gear carrier of the transmission connected to the motor end shield would be cast with an increased thickness or with reinforcing gussets or webs to resist the bending of the gear carrier. Unfortunately, beefing up the construction of the component parts of the motorized conveyor pulley significantly increases the cost of manufacturing the motorized conveyor pulley.
What is needed to overcome the problem of bending of motorized conveyor pulleys is an improved construction of the pulley that isolates the internal components of the motorized conveyor pulley from the bending loads without appreciably increasing the cost of manufacture of the internal components and the motorized conveyor pulley.
The motorized conveyor pulley of the invention eliminates or significantly reduces the bending of the cylindrical pulley drum due to the conveyor belt load and thereby isolates the internal component parts of the pulley from stresses due to bending. The motorized conveyor pulley of the invention is similar to prior art conveyor pulleys in that it is comprised of a cylindrical pulley drum having a hollow interior with end plates at the axially opposite ends of the drum. However, the axial thickness of the end plates is substantially increased. By increasing the thickness of the end plates, the axial length of the center bores passing through the end plates is also increased. The increase in the axial length of the center bores allows the positioning of pairs of bearings inside the center bores and on the stub shaft ends that pass through the center bores. In the preferred embodiment of the invention, the increased axial thickness of the end plates and the increased length of the end plate center bores allows the positioning of two axially spaced bearings in each of the center bores and on each of the stub shaft ends. The axial spacing of the pairs of bearings also allows the positioning of a shaft seal in each center bore between the pairs of bearings. In the preferred embodiment, the axial spacing allows the positioning of two shaft seals on each stub shaft providing a redundant system for preventing leakage of lubricant from the interior of the pulley drum. The use of two bearings mounting each end plate of the pulley drum on each of the stub shaft ends effectively unloads all of the internal components of the pulley from excessive loading due to belt tension bending. In an extreme comparison, the pair of stub shaft ends, their associated pairs of bearings and the end plates of the pulley drum they support may exist without any internal support required to satisfactorily take up the belt tension loading.